This invention relates to grippers for use with industrial robots.
Robots in industry today are used mostly to handle pieces, parts, equipment and material. Of critical importance in the design of a gripper for material handling is cycle time. When loading and unloading a machine with a robot, a short cycle time means a more effective utilization of the machine.
The use of a single gripper on a robot arm avoids the need of designing special multipurpose grippers. However, a single gripper might require the use of reorientation stands when transferring parts from one location to another, since motion limitations on how a single gripper may grasp a part does not permit the part to be picked up in the same orientation as required for insertion in a machine. Part reorientation results in an increase in cycle time.
In five axis robots with grippers in line with the robot arm, the parts feeder and the point of insertion of the part (machine chuck jaws, pallet, assembly fixture) must be along the center line of the robot arm. The center line restriction of five axis robots results in large space requirements when laying out the robot parts feeder and point of insertion, which in turn creates space problems particularly in retrofitting a robotic system with an existing machining center.
In handling a variety of parts using a single robot arm, the robot gripper and/or gripper fingers need to be changed, requiring a large inventory of specially designed grippers and/or fingers and incurring the associated retooling time.
Grippers normally have a parallel or a scissors arrangement with two moving surfaces coming together to grasp a part. Grippers of this type do not have compliance, that is, the ability to effectively grasp and hold any part within the full range of the grippers closing motion. When operating a robot with two moving jaws in a teach mode many attempts are required to properly position the gripper with the part precisely centered so that upon closing the grippers the part does not move. The motion of a robot arm has a repeatability typically of 0.005 of an inch, but centering a part by eye can typically be done only within 0.030 of an inch.
It is an object of the present invention to provide a gripper with compliance to eliminate many gripper and/or gripper finger changes.
It is a further object of the present invention to provide a multiple gripper for a 5 axis robot to eliminate the center line restriction for obtaining parts from a parts feeder and for part insertion.
It is still a further object of the present invention to provide a gripper which usually eliminates the need for part reorientation and achieves the accompanying reduction in cycle time.
It is another object of the present invention to provide a gripper which allows precise gripper positioning relative to the part to be grasped when operating the robot arm in a teach mode.